Universal route to optimal few- to single-cycle pulse generation in hollow-core fiber compressors.

Gas-filled hollow-core fiber (HCF) pulse post-compressors generating few- to single-cycle pulses are a key enabling tool for attosecond science and ultrafast spectroscopy. Achieving optimum performance in this regime can be extremely challenging due to the ultra-broad bandwidth of the pulses and the need of an adequate temporal diagnostic. These difficulties have hindered the full exploitation of HCF post-compressors, namely the generation of stable and high-quality near-Fourier-transform-limited pulses. Here we show that, independently of conditions such as the type of gas or the laser system used, there is a universal route to obtain the shortest stable output pulse down to the single-cycle regime. Numerical simulations and experimental measurements performed with the dispersion-scan technique reveal that, in quite general conditions, post-compressed pulses exhibit a residual third-order dispersion intrinsic to optimum nonlinear propagation within the fiber, in agreement with measurements independently performed in several laboratories around the world. The understanding of this effect and its adequate correction, e.g. using simple transparent optical media, enables achieving high-quality post-compressed pulses with only minor changes in existing setups. These optimized sources have impact in many fields of science and technology and should enable new and exciting applications in the few- to single-cycle pulse regime.

Single-shot implementation of dispersion-scan for the characterization of ultrashort laser pulses.

We demonstrate a single-shot ultrafast diagnostic, based on the dispersion-scan (d-scan) technique. In this implementation, rather than translating wedges to vary the dispersion as in scanning d-scan, the pulse to be measured experiences a spatially varying amount of dispersion in a prism. The resulting beam is then imaged into a second-harmonic generation crystal and an imaging spectrometer is used to measure the two-dimensional trace, which is analyzed using the d-scan retrieval algorithm. We compare the single-shot implementation with the scanning d-scan for the measurement of sub-3.5-fs pulses from a hollow core fiber pulse compressor. We show that the retrieval algorithm used to extract amplitude and phase of the pulse provides comparable results, proving the validity of the new single-shot implementation in the near single-cycle regime.

Carrier-envelope-phase insensitivity in high-order harmonic generation driven by few-cycle laser pulses.

We present evidence for self-stabilization of the relative spectral phase of high-order harmonic emission against intensity variations of the driving field. Our results demonstrate that, near the laser focus, phase matching of the harmonic field from a macroscopic target can compensate for the intensity dependence of the intrinsic phase of the harmonics emitted by a single radiator. As a consequence, we show experimentally and theoretically the insensitivity of the harmonic spectra produced at the laser focus against variations of the carrier-envelope phase (CEP) of a sub-two-cycle driving field. In addition, the associated attosecond pulse trains exhibit phase locking against CEP changes of the few-cycle driver.

Temporal and spectral structure of the infrared pulse during the high order harmonic generation.

We present, for the first time, the complete pulse characterization of the infrared pulse after generating harmonics. A systematic study of the high harmonic generation process, and the generating infrared pulse characterization, has been done by changing the focus-gas-jet relative position. We have concluded, supported by nonlinear propagation simulations, that there is a correlation between the spectral and temporal nonlinear evolution of the infrared generating field and the structures shown in the harmonic signal. We have identified two different pressure regimes: the low pressure regime, characterized by the effects produced by the plasma generated by the infrared pulse, and the high pressure regime where the plasma and the Kerr effect generated by the infrared field are both present. These observations highlight the important role played by the nonlinear propagation of the generating field in the high harmonic generation context.

Population-based surveillance and a case-control study of risk factors for endemic lymphocutaneous sporotrichosis in Peru.

Population-based surveillance and a case-control study were conducted in Abancay, Peru, to estimate the burden of disease and to determine risk factors for sporadic lymphocutaneous sporotrichosis (LS). Laboratory records from local hospitals were reviewed for the years of 1997 and 1998, and prospective surveillance was conducted for the period of September 1998 through September 1999. A case-control study was conducted with 2 matched control subjects per case patient. The mean annual incidence was 98 cases per 100,000 persons. Children had an incidence 3 times higher than that for adults and were more likely to have LS lesions on the face and neck. Identified risk factors included owning a cat, playing in crop fields, having a dirt floor in the house, working mainly outdoors, and having a ceiling made of raw wood or conditions associated with a lower socioeconomic status. Decreased environmental exposure, such wearing protective clothing during construction activities for adults or limiting contact with cats and soil for children, and improvements in living spaces may decrease the incidence of LS.

Sporotrichosis in Peru: description of an area of hyperendemicity.

Sporotrichosis is a sporadic and rare mycotic infection in most of the developed world. In many parts of the developing world, sporotrichosis is much more commonly recognized, but epidemiological data are generally lacking from these regions. We report epidemiological, clinical, and treatment data from 238 cases of culture-proven sporotrichosis occurring in a relatively remote area of the south central highlands of Peru that were retrospectively collected during 1995-1997. Most cases (60%) occurred in children aged

Treatment of cutaneous sporotrichosis with one daily dose of potassium iodide.

BACKGROUND: Recommended treatment for cutaneous sporotrichosis consists of a saturated solution of potassium iodide (SSKI) administered in three daily doses (tid). Because compliance with this regimen has been a problem in our previous experience, we evaluated the use of one daily (qd) full dose of SSKI. METHODS: Patients with culture-confirmed cutaneous sporotrichosis were entered in a randomized, nonblinded study to compare the safety and efficacy of qd vs. tid dosage of SSKI. RESULTS: Fifty-seven patients were enrolled to receive either qd (29) or tid (28) SSKI. Three (1 in the qd and 2 in the tid group) were not compliant with the assigned regimen. Side effects were common but mild in both treatment groups (61% in the qd and 42% in the tid group, P = 0.17); treatment had to be discontinued because of side effects in 3 cases (2 in the qd and 1 in the tid group). Overall 26 (89.6%) and 25 (89.2%) of the individuals initially assigned to the qd and tid dosing schedule, respectively, were cured by the treatment. No relapse was detected after 45 days of follow-up. CONCLUSION: These findings suggest that a single daily full dose of SSKI appears to be appropriate therapy for cutaneous sporotrichosis; further studies with larger numbers of patients are required.